The kinetics of G-CSF mobilization of CD34+ cells in healthy people

When healthy people are given granulocyte colony stimulating factor (G-CSF) for 10 days the number of CD34+ cells in the peripheral blood begins to increase on the fourth day, reaches a maximum on the sixth day and then decreases. In this study, we further define the time and variability of peak mobilization of CD34+ cells. Twenty-two healthy people were given G-CSF (7.5 or 10 μg kg^-1 day^-1) subcutaneously each morning for 5 days and peripheral blood CD34+ cell counts were analysed immediately prior to the fourth (day 4) and fifth (day 5) G-CSF injection and 24 h after the fifth injection (Day 6). White blood cell (WBC) and neutrophil counts were greatest on day 6 [WBC = 43.8 ± 13.9 x 10⁹ L^-1 (mean ± 1 SD) and neutrophils = 36.6 ± 12.8 x 10⁹ L^-1]. In contrast the CD34+ cell counts on day 6 (107 ± 104 x 10⁶ L^-1) were less than on day 5 (128 ± 136 x 10⁶ L^-1) (p = 0.048) but still greater than on day 4 (60.7 ± 40.2 x 10⁶ L^-1) (P < 0.0001). The CD34+ cell counts of 10 donors were measured 2, 4 and 6 h after the fifth injection to determine if the counts increased further between days 5 and 6. The number of CD34+ cells in the blood on day 5 2 h after the fifth injection (193 ± 277 x 10⁶ L^-1) was greater than the number prior to the injection (158 ± 190 x 10⁶ L^-1), 4 h post-injection (139 ± 158 x 10⁶ L^-1) and 6 h post-injection (170 ± 236 x 10⁶ L^-1), but the differences were not significant (P = 0.29, 0.25 and 0.45). The number of CD34+ cells in the blood of 12 people were measured before and after the fourth G-CSF dose. Prior to the day 4 injection the CD34+ count was 61 ± 40 x 10⁶ L^-1. At 2, 4 and 6 h the counts were 60 ± 40, 61 ± 29 and 64 ± 30 x 10⁶ L^-1, respectively, and the differences were not significant (P = 0.99, P = 0.98, and P = 0.73). In conclusion, when healthy volunteers are given daily G-CSF injections, the number of mobilized CD34+ cells was the greatest on day 5, slightly less on day 6 and the least on day 4. If only one PBSC component is needed, PBSCs can be collected on day 5 after only 4 days of G-CSF. If PBSC components are collected on both days 5 and 6, the fifth dose can be given either before or after the collection of the first PBSC component.